Posted
by
samzenpus
on Friday July 25, 2014 @04:34AM
from the skin-of-your-teeth dept.

sciencehabit writes In mid-October, a comet sweeping through our inner solar system for the first time will pass near Mars—so close, in fact, that if it were buzzing Earth at the same distance it would fly by well inside our moon's orbit. While material spewing from the icy visitor probably won't trigger the colossal meteor showers on the Red Planet that some scientists predicted, dust and water vapor may still slam into Mars, briefly heating up its atmosphere and threatening orbiting spacecraft. However it affects the planet, the comet should give scientists their closest view yet of a near-pristine visitor from the outer edges of our solar system.

The theory is that there's a big (really big) store of comets in Oort's cloud on the far outskirts of the solar system. They have never been near to the Sun having been formed far from the centre. Once their movements are perturbed they may go towards the Sun.

Can I take a moment to talk about how mind-crushingly vast the Oort cloud is? It doesn't begin until something on the order of 100 times the orbit of the furthest known dwarf planets, and then it goes out about a quarter of the way to the nearest neighbouring star. It's so far away that, being composed of inert space junk, we have no direct observational evidence of its existence. I mean, space is big, big to the point where thinking hard about Jupiter makes my temples ache, but the Oort cloud is something else entirely. And that's just an object on a planetary system scale!

I don't understand the concept of first pass. Do they really mean "first pass ever" which I suppose would also mean humanity will never ever interact with this comet ever?

[emphasis mine]
Why? (Assuming humanity lives in harmony on Earth for another few million years)
It's non-periodic (the 'C' in C/2013 A1 (Siding Spring)) comet, so as far as we know, it will be the first and only pass through the inner Solar System.

If this happened (optimistically) 50 years from now, we'd be able to deflect the comet to HIT mars, thus delivering a lot of water and warming things up a bit. (Only, I'm afraid, a little bit of terraforming, it would probably take thousands of such comet strikes to make the planet "habitable"). Or we could make it hit one of the moons and, if done very carefully, could deliver said water to possible Mars Moon colonists (but they'd have to find a way to keep the resulting fragments from ruining near-Mars space for space travels).

More realistically, I wonder if NASA (and the ESA) have plans to move their spacecraft for best viewing. If they're worried about damage, they could have them be on the other side of the planet when it makes its closest approach. If there are any spacecraft that are on their "last legs" (low propellent, malfunctioning equipment, no more spare reaction wheels), perhaps they could even make a very risky close approach!

I expect there will be some great images! (If the HiRes camera on the Mars Reconnaissance Orbiter can take 1m resolutions of Mars from orbit, it surely will be able to take great pictures of a comet only a few tens of thousands of kilometers away).

So what? You're not going to alter the planet's trajectory enough to be an issue just by throwing a few pebbles at it. Especially if those pebbles are spread fairly evenly across multiple years so that the perturbations tend to cancel each other out. Even if it was just one ginormous impact that is unlikely to necessitate anything more than altering a few decimal places in the orbital parameters to keep our planetariums accurate.

Remember - both Earth and Mars have been hit by truly *massive* bodies in th

We have fusion now... We can start a fusion reaction pretty much whenever we want. The problem is we cannot create a sustained fusion reaction that nets us industrial levels of energy and do it in a cost effective way.

What the fusion problem really becomes is a materials and technique question. How do you safely sustain a fusion reaction long enough in some kind of container so you can collect the excess energy it creates without having to replace the expensive container too often. So we have a containme

We have fusion now... We can start a fusion reaction pretty much whenever we want. The problem is we cannot create a sustained fusion reaction that nets us industrial levels of energy and do it in a cost effective way.

Then, it's pretty useless as an energy solution, isn't it?

When I say "I'll believe it when I see it", I don't mean some bench prototype which doesn't deliver, I mean a real, functioning system.

And we've been "a few years away" from having that from decades now. Until proven otherwise, I will

Can't argue with that... Personally, I think that funding fusion research is something we should be doing instead of messing around with tax credits for windmills and solar panels. Where I don't figure the "We are almost there!" press is true either, it *could* be if we really put some resources into this research and development and where I'm not foolish enough to think having a working fusion plant would be the end all be all of energy production, it sure would be a step in the right direction.

Well, if they would stop cutting back funding to fusion research we probably would have it by now - TOKAMAK advances on that front have been keeping pace fairly consistently with initial estimates in terms of progress per dollar, but funding has been decreasing exponentially almost from the day of the initial 20-year estimate.

On the other hand the fringe projects seem to be making some pretty impressive progress on potentially far more efficient fusion strategies. EMC2's polywell fusor seems to have confirm

While the solar wind will blow away the atmosphere in a (perhaps) short time geologically speaking, in a human timescale it would likely take thousands of years. By then, the humans could have implemented a giant electromagnetic shield (powered by sharks with frickin lasers) or have developed wormholes to directly transfer water from the water from Jupiter's moons or have migrated to the far reaches of the galaxy. Or have gone extinct.

Mars didn't become the dry desert it is today in an instant, I believe

Actually IIRC Mars may have been fairly Earthlike (at least geologically) as recently as ten million years ago, which would suggest several billion years of warm, wet history before it became the frozen desert we see today.

Not necessarily - Venus has no geomagnetic shielding either, and gets hit by a far denser solar wind. In fairness it's thick ionosphere interacts with the solar wind to generate an induced magnetosphere, but such a thing could potentially be engineered elsewhere.

Plus, even without a magnetosphere we're talking about a process that takes thousands, maybe even millions of years to strip a planet of it's atmosphere - if we can build it up in the first place we should be able to compensate for the losses easily

Sure we do - Solar, wind, nuclear, etc. are all perfectly viable energy sources, they're just currently more expensive than fossil fuels (especially when you factor in battery costs) so market forces have continued to favor those. Prices continue to fall though, and now we have Aquion selling batteries for 1/10th the amortized cost of lead-acid for stationary applications, which will ti the scale even further. And if we stopped publicly funding the various tax-breaks, subsidies, environmental damage immun

The orbiters do not have the fuel to move out of the way and besides it will be a big cloud of dust and vapor and ice; impossible to avoid. They best that can be done is orient the spacecraft in some way to minimize the potential damage.
As far as images, well maybe. The orbiters are designed to look down, not up so some fancy maneuvering will be needed but I think it can be done. The photos will show a fuzzy blob, but more interesting will the readings from the spectrometers and other instruments. MSL

If this happened (optimistically) 50 years from now, we'd be able to deflect the comet to HIT mars, thus delivering a lot of water and warming things up a bit. (Only, I'm afraid, a little bit of terraforming, it would probably take thousands of such comet strikes to make the planet "habitable").

The problem with doing this to Mars is that it has a very small magnetic field to protect it and radiation pretty much streams in to the surface unfiltered. Where it would help to add water and gases to the atmosphere, without a magnetic field to protect it, these would eventually be stripped away by the solar wind and you'd be back to square one.

Then there is the technical problems involved in figuring out how you can get enough of a push on some unknown constantly changing mass of ice and dust to make t

The moon is about 384,000km away from the earth. The earth is about 6,400 km wide. That means only 0.027% of the area inside the moon's orbit is occupied by the earth. So this "near miss" was better described as a 1 in 3600 to one odds of hitting mars.

Has anyone calculated what effect Mars's gravity will have on the comets trajectory? Will it gain/lose velocity relative to the sun? Will it's orbit be narrower/wider (will the close encounter send the rock tumbling out of the system again, or will it smash into the sun)? Or will the forces involved be simply too small to have the tiniest effect?

I think comets tend to be moving far to fast for a gravitational slingshot to have much effect. Your basic gravitational slingsot involves a near-miss head-on collision with a planet racing towards you. You whip around the planet and fly back roughly the way you came with your initial speed plus the orbital speed of the planet. Obviously you can do a less dramatic maneuver, but you only get a fraction of the speed boost.

Comets meanwhile have typically been falling towards the sun from a good portion of a